This invention relates to voltage regulation of electric generators and, more particularly, to a method and circuit for regulating the output voltage of an electric generator which is subject to varying loads and may be driven at varying speeds.
Typical voltage regulators which are used to regulate the output voltage of electric generators include a sensing circuit that produces a voltage signal proportional to the AC or DC output of the generator. This signal is subtracted from a reference signal to develop a signal proportional to the error in the generator output. A compensator modifies the gain of the voltage regulator control loop. The output of the compensator is amplified and used to control the exciter field current in the generator. The output of the generator is proportional to the exciter field current. The gain and response of each element in the control loop can be measured and the compensator can be designed to achieve the desired transient response in accordance with well known feedback control methods.
In certain electrical systems, such as those found in aircraft, the generator must operate over a wide speed range. Since the gain (ratio of the output voltage to exciter field current) of a generator is proportional to its rotational speed and decreases as load is applied, voltage regulators constructed as discussed above may produce an unacceptable transient response as a load is applied or removed from the generator at various speeds. For example, when a load is applied to a generator operating near the low end of its operating speed range, the generator output initially decreases and slowly recovers because the gain of the voltage control loop is relatively low. The gain cannot be significantly increased because a load removal at high speed would result in a seriously underdamped condition. There is a considerable difference in transient response over the required speed and load range. The present invention seeks to provide a voltage regulator which improves generator transient response over the expected operating speed and load range.